Steam reforming plants for hydrogen fall into two general areas depending on the type of carbon dioxide removal.
Hydrogen plants built since the late-1980s tend to use Pressure Swing Absorption (PSA) for purification, while older hydrogen plants use wet scrubbing.
The most common configuration for a wet scrubbing hydrogen plant uses two stages of shift conversion, followed by wet scrubbing and methanation. A variety of scrubbing processes are used, typically based on an amine or on potassium carbonate. Product purity depends mainly on the amount of methane leaving the reformer.
A PSA-based hydrogen plant will typically employ a steam reformer, a single high-temperature shift converter, gas cooling, and finally purification by PSA. The product purity of a PSA plant is not linked to reforming conditions as in a wet scrubbing plant. This type of plant will typically yield 99.99% purity hydrogen. To achieve higher purity hydrogen that is required for electronics, food and float glass industries (i.e., 99.9999% or higher), the PSA is either run at a lower recovery rate of less than 75% or the PSA output is run through a cryogenic system where the purity is increased.
Existing PSA-based hydrogen plants, even when designed to supply small to moderate consumers of hydrogen, are based on the same platform utilized for large hydrogen plants and are dependent upon outside sources of electrical power. Even short power outages can cause such plants to be inoperative for hours, where reformers need to be ramped back up to temperature and where PSA systems need to be brought back to full operation.
It is further noted that the hydrogen production methods outlined above depend upon fossil fuels to produce hydrogen. Reliance upon fossil fuels, however, is problematic for a number of reasons. First, fossil fuels imported from foreign sources have been the subject of exorbitant price increases and supply volume limitations. Second, the stored energy present in these fuels may be released only during combustion, which serves to release toxic pollutants into the atmosphere. It therefore appears reasonable from both an economic and environmental standpoint to develop alternative sources of fuel.
Thus, a need exists for a self-contained and streamlined hydrogen generation system that does not rely upon fossil fuels to produce hydrogen.
It is therefore an object of the present invention to provide such a system.
It is a more specific object of the present invention to provide a more reliable and cost effective system for generating renewable sources of methane and high purity hydrogen.
It is yet a more specific object to provide a self-contained methane and/or high purity hydrogen generation system that is streamlined in design and that converts organic materials such as animal waste into the desired product gas or gases.